Polishing fluid and polishing method

ABSTRACT

Provided is a polishing fluid that has a fast polishing rate, and can selectively suppress polishing of layers including polysilicon or modified polysilicon during the chemical mechanical polishing in the manufacture of semiconductor integrated circuits, and a polishing method using the same. A polishing fluid used for the chemical mechanical polishing in which each of the components represented by the following (1) and (2) is included, the pH is 1.5 to 5.0, and a polishing workpiece can be polished in a range of a ratio represented by RR (other)/RR (p-Si) when the polishing rate of the first layer is RR (p-Si), and the polishing rate of the second layer is RR (other) of 1.5 to 200.
         (1) Colloidal silica particles   (2) At least one inorganic phosphate compound selected from phosphoric acid, pyrophosphoric acid, and polyphosphoric acid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing fluid used in a step ofmanufacturing a semiconductor integrated circuit, and a polishing methodusing the same.

2. Description of the Related Art

Recently, there has been demand for an increase in density and anincrease in integration by means of miniaturizing and laminating wiringsin pursuit of size reduction and increased speed in the development ofsemiconductor devices represented by semiconductor integrated circuits(hereinafter, sometimes, referred to as “LSI”). A variety of techniques,such as chemical mechanical polishing (hereinafter, sometimes referredto as “CMP”), have been used as techniques for this pursuit. The CMP isan essential technique when carrying out the surface flattening of afilm workpiece, such as an interlayer insulation film, plug formation,formation of embedded metal wirings, and the like, and the CMP carriesout the flattening and the like of substrates.

In an ordinary method of the CMP, a polishing pad is attached to a roundpolishing platen, the surface of the polishing pad is soaked with apolishing fluid, the surface (surface to be polished) of a substrate(wafer) is pressed to the pad, and both the polishing platen and thesubstrate are rotated in a state in which a predetermined pressure(polishing pressure) is applied from the rear surface of the substrate,thereby flattening the surface of the substrate by mechanical frictiongenerated.

In recent years, the CMP has been applied to each step in themanufacture of semiconductors, and an example of an aspect thereofincludes an application to the gate forming step in the manufacture oftransistors.

In this case, gates mainly made of modified polysilicon obtained byinjecting impurities, such as B, to polysilicon have been manufacturedfor transistors in the related art, but ongoing studies are beingcarried out regarding the application of high-dielectric constant gateinsulation films (high-k films) and metal gate electrodes, instead ofpolysilicon in the related art, to transistors of 45 nm-generation orlater to satisfy both the reduction of power consumption during standbyand high-current operation capabilities. Several methods have beensuggested as technologies in which the above is applied. For example, amethod in which a dummy gate insulation film and a dummy gate electrodeare formed, a source drain diffusion layer is formed by injectingimpurities to a polycrystalline silicon film in a self-aligning manner,the dummy gate insulation film and the dummy gate electrode are removed,and a high-dielectric constant gate insulation film and a metal gateelectrode are then formed is suggested (for example, refer toJP2007-12922A).

In addition, several techniques have been suggested regarding the methodof forming a metal gate electrode. A fully silicided gate (hereinafter,referred to as “FUSI gate”) is one of the candidates thereof. The FUSIgate is formed by siliciding a gate electrode formed of polysilicon,similarly to the CMOS process in the related art, but the entire gateelectrode is silicided in the FUSI while only the top portion of thegate electrode was silicided in the related art. The FUSI has a largemerit in building processes in comparison to the method in which a metalgate electrode is formed by the damascene process since the know how ofthe CMOS process in the related art becomes useful.

In recent years, it has been suggested to selectively perform the CMP onpolysilicon and the like and the second and the third materials thatcover the periphery of the polysilicon when a gate is formed using theabove polysilicon or modified polysilicon (hereinafter referred tosimply and collectively as “polysilicon and the like”) (for example,refer to JP-H06-124932A (JP1994-124932A) and JP2009-540575A). However,when a polishing workpiece including polysilicon and the like ispolished by the CMP using a well-known polishing fluid in the relatedart, there is a problem in that polysilicon and the like which themanufacturer wants to remain as a gate material are excessivelypolished, which may, furthermore, cause performance degradation or thelike of the obtained LSI.

For the purpose of solving the problems of the performance degradationand the like of an LSI, JP2009-290126A discloses a polishing fluid thatis used for the chemical mechanical polishing of polishing workpieceswhich are configured to have at least a first layer includingpolysilicon or modified polysilicon, and a second layer including atleast one selected from a group consisting of silicon oxide, siliconnitride, silicon carbide, silicon carbonitride, silicon oxycarbide, andsilicon oxynitride; contains colloidal silica particles, an organicacid, and an anionic surfactant; has a pH of 1.5 to 7.0; and canselectively polish the second layer with respect to the first layer.

SUMMARY OF THE INVENTION

A certain degree of effect with respect to the problem of theperformance degradation and the like of an LSI can be obtained by usingthe polishing fluid disclosed in JP2009-290126A, but there is demand foradditional improvement of the effect.

Therefore, an object of the invention is to provide a polishing fluidthat has a fast polishing rate, and can selectively suppress polishingof layers including polysilicon or modified polysilicon during thechemical mechanical polishing in the manufacture of semiconductorintegrated circuits, and, furthermore, realizes high aging stabilityduring the storage of the polishing fluid (properties of suppressing andpreventing degradation over passage of time), and a polishing methodusing the same.

The detailed means for solving the above problems are as follows.

[1] A polishing fluid used for the chemical mechanical polishing ofsemiconductor substrates that are configured to have at least a firstlayer including polysilicon or modified polysilicon, and a second layerincluding at least one selected from a group consisting of siliconoxide, silicon nitride, silicon carbide, silicon carbonitride, siliconoxycarbide, and silicon oxynitride,

in which each of the components represented by the following (1) and (2)is included, the pH is 1.5 to 5.0, and a polishing workpiece can bepolished in a range of a ratio represented by RR (other)/RR (p-Si) whenthe polishing rate of the first layer is RR (p-Si), and the polishingrate of the second layer is RR (other) of 1.5 to 200.

(1) Colloidal silica particles

(2) At least one inorganic phosphate compound selected from phosphoricacid, pyrophosphoric acid, and polyphosphoric acid.

[2] The polishing fluid according to [1] further including an anionicsurfactant represented by the general formula (I) as a third component.

R¹—SO₃X  (I)

[In the general formula, ‘R¹’ represents alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, all of which have acarbon number of 6 to 30, and groups formed by combining 2 or more ofthe above groups. ‘X’ represents a hydrogen atom, lithium, sodium,potassium, an ammonium cation, and quaternary ammonium cations.]

[3] The polishing fluid according to [2] including at least one selectedfrom a group consisting of compounds represented by the followinggeneral formula (II), general formula (III), general formula (IV), andgeneral formula (V) instead of or together with the anion surfactantrepresented by the general formula (I) as the third component.

R¹—O—SO₃X  (II)

[In the general formula (III), ‘R¹’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl grams, all of which havea carbon number of 6 to 30, or groups formed by combining 2 or more ofthe above groups. ‘X’ represents a hydrogen atom, sodium, potassium, anammonium cation, quaternary ammonium cations, diethanolamine, ortriethanolamine.]

R²—O—(CH₂CH₂O)_(n)—SO₃X  (III)

[In the general formula (III), ‘R²’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups. ‘n’ represents an integer of 1 to 10. ‘X’represents the same as in the general formula (II).]

[In the general formula (IV), ‘R³’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups, ‘X’ represents the same as in the general formula(II), and a plurality of Xs may be mutually the same or different.]

[In the general formula (V), ‘R⁴’ represents alkylene groups, alkynylenegroups, cycloalkylene groups, arylene groups, alkylene oxide groups, allof which have a carbon number of 1 to 20, or groups formed by combining2 or more of the above groups. ‘R⁵ to R⁹’ independently represent any ofa hydrogen atom, a hydroxyl group, alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, sulfo groups, carboxylgroups, all of which have a carbon number of 1 to 30, and hydrocarbongroups including the above. ‘X’ represents the same as in the generalformula (II).]

[4] The polishing fluid according to any of [1] to [3], in which theconcentration of the colloidal silica particles is 0.1% by mass to 10%by mass with respect to the total mass of the polishing fluid.

[5] The polishing fluid according to any of [1] to [4], in which theaverage primary particle diameter of the colloidal silica particles is 5nm to 100 nm, and the average secondary particle diameter is in a rangeof 10 nm to 300 nm.

[6] The polishing fluid according to any of [1] to [5], in which thecolloidal silica particles have a negative ξ potential, and the ξpotential is −50 mV to −5 mV.

[7] The polishing fluid according to any of [1] to [6], in which thecontent of the inorganic phosphate compound is 0.001% by mass to 10% bymass.

[8] The polishing fluid according to any of [2] to [7], in which theconcentration of the anionic surfactant is 0.001% by mass to 1% by masswith respect to the total mass of the polishing fluid.

[9] The polishing fluid according to any of [2] to [8], in which theanionic surfactant is a multivalent anionic surfactant.

[10] The polishing fluid according to any of [1] to [9], in which theelectrical conductivity of the polishing fluid is in a range of 0.01(mS/cm) to 12 (mS/cm).

[11] A method of manufacturing a semiconductor device, in which, eachtime the chemical mechanical polishing (CMP) method is carried out topolish the surface of a semiconductor substrate that is configured tohave at least a first layer including polysilicon or modifiedpolysilicon, and a second layer including at least one selected from agroup consisting of silicon oxide, silicon nitride, silicon carbide,silicon carbonitride, silicon oxycarbide, and silicon oxynitride, aprocessing treatment including

(a) a step in which a polishing fluid including each of the componentsof the following (1) and (2) and having a pH of 1.5 to 5.0 is prepared,

(b) a step in which the polishing fluid is supplied to the surface ofthe semiconductor substrate, and a polishing pad is brought into contactwith the surface of the semiconductor substrate, and

(c) a step in which, each time the first layer and the second layer ofthe semiconductor substrate are polished, the polishing pad and thesemiconductor substrate are relatively moved so that a polishingworkpiece can be polished in a range of a ratio represented by RR(other)/RR (p-Si) when the polishing rate of the first layer is RR(p-Si), and the polishing rate of the second layer is RR (other) of 1.5to 200 while the polishing pad is in continuous contact with the surfaceof the semiconductor substrate through the polishing fluid for a timesufficient enough to polish the second layer is carried out.

(1) Colloidal silica particles

(2) At least one inorganic phosphate compound selected from phosphoricacid, pyrophosphoric acid, and polyphosphoric acid.

[12] The method of manufacturing a semiconductor device according to[11] further including compounds selected from a group consisting ofcompounds represented by the general formulas (I) to (V) as a thirdcomponent.

R¹—SO₃X  (I)

[In the general formula (I), ‘R¹’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, and groups formed by combining 2 ormore of the above groups. ‘X’ represents a hydrogen atom, lithium,sodium, potassium, an ammonium cation, and quaternary ammonium cations.]

R¹—O—SO₃X  (II)

[In the general formula (II), ‘R¹’ represents the same as the generalformula (I). ‘X’ represents a hydrogen atom, sodium, potassium, anammonium cation, quaternary ammonium cations, diethanolamine, ortriethanolamine.]

R²—O—(CH₂CH₂O)_(n)—SO₃X  (III)

[In the general formula (III), ‘R²’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups. ‘n’ represents an integer of 1 to 10. ‘X’represents the same as in the general formula (II).]

[In the general formula (IV), ‘R³’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups, ‘X’ represents the same as in the general formula(II), and a plurality of Xs may be mutually the same or different.]

[In the general formula (V), ‘R⁴’ represents alkylene groups, alkynylenegroups, cycloalkylene groups, arylene groups, alkylene oxide groups, allof which have a carbon number of 1 to 20, or groups formed by combining2 or more of the above groups. ‘R⁵ to R⁹’ independently represent any ofa hydrogen atom, a hydroxyl group, alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, sulfo groups, carboxylgroups, all of which have a carbon number of 1 to 30, and hydrocarbongroups including the above. ‘X’ represents the same as in the generalformula (II).]

According to the invention, it is possible to provide a polishing fluidthat has a fast polishing rate, and can selectively suppress polishingof layers including polysilicon or modified polysilicon during thechemical mechanical polishing in the manufacture of semiconductorintegrated circuits, and, furthermore, realizes high aging stabilitywhile the polishing fluid is stored, and a polishing method using thesame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a group of cross-sectional views showing a substrate as anembodiment to which the polishing fluid of the invention is applied, inwhich FIG. 1A shows a state before polishing and FIG. 1B shows a stateafter polishing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the polishing fluid of the invention contains a combinationof colloidal silica particles, an inorganic phosphate compound, and aspecific anionic surfactant according to necessity, and has a pHadjusted to a predetermined range. Thereby, it is possible to achievesuperior polishing in the CMP step to the polishing fluids suggested inthe related art, and, particularly, an excellent effect, by which thepolishing rate of polysilicon or modified polysilicon can be selectivelysuppressed while rapid polishing is maintained across the entireworkpiece, is exhibited. Hereinafter the invention will be described indetail based on preferred embodiments of the invention.

[Polishing Fluid]

The polishing fluid of the invention contains each of the followingcomponents, and the pH is 1.5 to 5.0.

(1) Colloidal silica particles

(2) At least one inorganic phosphate compound selected from phosphoricacid, pyrophosphoric acid, and polyphosphoric acid.

The “polishing fluid” in the invention refers to not only polishingfluids used for polishing (that is, polishing fluids diluted accordingto necessity) but also the concentrated solutions of polishing fluids.The concentrated solutions or concentrated polishing fluids refer topolishing fluids in which the concentration of the solute is adjusted tohigher than that of polishing fluids used for polishing, and polishingfluids that are diluted by water, an aqueous solution, or the like, andthen used for polishing. The dilution is normally 1 time by volume to 20times by volume. In the present specification, the terms “concentrated”and “concentrated solution” are used in accordance with the practicalexpression having a meaning of “denser” and “denser fluid” than in usagestates, and used in a different manner from the general meaning of theterms which accompany physical concentration operations, such asvaporization. In addition, the compounds in the invention refer to notonly compounds represented by the chemical equations and the like, butalso the salts and ions thereof.

The polishing fluid of the invention is a polishing fluid that ispreferably used when formation of a gate electrode is carried out by theCMP in a semiconductor integrated circuit, for which polysilicon ormodified polysilicon is applied as an electrode material. Morespecifically, the polishing fluid of the invention can be used for thechemical mechanical polishing of a polishing workpiece that isconfigured to have at least a first layer including polysilicon ormodified polysilicon, and a second layer including at least one selectedfrom a group consisting of silicon oxide, silicon nitride, siliconcarbide, silicon carbonitride, silicon oxycarbide, and siliconoxynitride during the flattening step in the manufacture ofsemiconductor integrated circuits.

The polishing fluid of the invention contains each of the componentsrepresented by (1) or (2), and has a pH of 1.5 to 5.0. Thereby, thesecond layer including at least one selected from a group consisting ofsilicon oxide, silicon nitride, silicon carbide, silicon carbonitride,silicon oxycarbide, and silicon oxynitride can be selectively polishedwith respect to the first layer including polysilicon or modifiedpolysilicon.

With regard to the selective polishing of the second layer with respectto the first layer, the polishing fluid of the invention is preferably apolishing fluid that can polish a polishing workpiece in a range of aratio represented by RR (other)/RR (p-Si) when the polishing rate of thefirst layer is RR (p-Si), and the polishing rate of the second layer isRR (other) of 1.5 to 200. The ratio represented by RR (other)/RR (p-Si)is preferably in a range of 3 to 10. When the ratio represented by RR(other)/RR (p-Si) is in the above range, undesired polishing withrespect to the first layer can be suppressed, and the uneven separationof the first layer caused by an excessive stress applied to the filminterface between the first layer and the base layer during polishingcan also be suppressed effectively.

Therefore, the use of the polishing fluid of the invention can allowrapid polishing of layers including silicon-based materials other thanpolysilicon or modified polysilicon, for which rapid polishing isrequired, without excessively polishing a gate electrode when a gateelectrode configured to include polysilicon or modified polysilicon isformed by the CMP in the manufacture of LSI.

[Colloidal Silica Particles]

The polishing fluid of the invention contains colloidal silicaparticles, which preferably exhibit a negative ξ potential at thesurfaces at least as a part of abrasive grains. The colloidal silicaparticles are not particularly limited, but are preferably colloidalsilica particles exhibiting a negative ξ potential at the surfaces by ananionic compound absorbed on the surfaces of the colloidal silicaparticles having positive electric charges. That is, a preferable formof the colloidal silica particles is that the colloidal silica particleshaving positive electric charges and an anionic compound are combined,and the anionic compound is absorbed on the surfaces of the colloidalsilica particles in the polishing fluid system, thereby exhibiting anegative ξ potential at the surfaces of the colloidal silica particles.

As such, colloidal silica particles obtained by the hydrolysis of alkoxysilane containing no impurities, such as alkali metals, inside theparticles are preferred as the colloidal silica particles that modify orimprove the surfaces. On the other hand, colloidal silica particlesmanufactured by a method in which alkali metal is removed from anaqueous solution of alkali silicate can also be used; however, in thiscase, there is a concern that alkali metal remaining inside theparticles will be gradually ejected and affect polishing performance.From such a viewpoint, colloidal silica particles obtained by thehydrolysis of alkoxy-silanes are more preferred as a raw material.

(Anion Compound)

Firstly, a colloidal silica particle having an anionic compound absorbedon the surface, which is one of the colloidal silica particlesexhibiting a negative ξ potential at the surface, will be described.

The anionic compound that is used here may be any of ordinary anioniccompounds, and may be an inorganic anionic compound or an organicanionic compound. However, the anionic surfactant as described below isnot included.

The concentration of the anionic compound in the polishing fluid ispreferably 0.00005% by mass to 1% by mass, more preferably 0.0001% bymass to 1% by mass, and particularly preferably 0.001% by mass to 1% bymass with respect to the total mass of the polishing fluid from theviewpoint of forming a negative ξ potential at the surfaces of thecolloidal silica particles and controlling the polishing rate.

The fact that colloidal silica particles exhibiting a negative ξpotential at the surfaces can be created by making an anionic compoundwork at the colloidal silica particles having positive electric chargescan be confirmed as follows.

That is, it can be confirmed by checking, when a polishing fluid B isobtained by adding the anionic compound to a polishing fluid Acontaining an oxidant and a corrosion inhibitor, whether the polishingrate of the polishing fluid B becomes 80% or lower of the polishing rateof the polishing fluid A, which is the polishing fluid before theanionic compound is added. The preferable polishing rate is 50% or lowerof the polishing rate when the polishing fluid A is used.

The above method makes it possible to confirm that colloidal silicaparticles exhibiting a negative ξ potential at the surfaces are formed,and polishing selectivity is improved by the colloidal silica particlesexhibiting a negative ξ potential at the surfaces.

The compound and the colloidal silica particles may be merely mixed inorder to make the above anionic compound absorbed on the surfaces of thecolloidal silica particles.

Thereby, the anionic compound having the above structure is absorbed onthe surfaces of the colloidal silica particles having a slight number ofnegative electric charges, and the colloidal silica particles exhibitinga negative ξ potential at the surface are obtained.

Here, the ξ potential at the surfaces of the colloidal silica particlescan be measured by a method, such as the electrophoresis method and theultrasonic oscillation method, in the invention. Examples of specificmeasuring instruments that can be used include DT-1200 (manufactured byNihon Rufuto Co., Ltd.).

The range of the ξ potential is not particularly limited, but ispreferably −50 mV to −3 mV, more preferably −30 mV to −3 mV, andparticularly preferably −20 mV to −5 mV.

The particle diameter of the colloidal silica particles, which become araw material, is appropriately selected according to the purpose of use.The average primary particle diameter is preferably in a range of 5 nmto 100 nm, more preferably in a range of 10 nm to 100 nm, and furtherpreferably in a range of 10 nm to 80 nm as the particle diameter of thecolloidal silica particles. In addition, the average secondary particlediameter of the colloidal silica particles is preferably in a range of10 nm to 300 nm, more preferably in a range of 20 nm to 300 nm, andfurther preferably in a range of 20 nm to 200 nm.

A particularly preferred embodiment of the colloidal silica particles inthe invention has an average primary particle diameter in a range of 5nm to 100 nm and an average secondary particle diameter in a range of 10nm to 300 nm.

The occurrence of polishing flaws can be effectively suppressed when theparticle diameter of the colloidal silica particles is in the aboverange.

Here, the average primary particle diameter of the colloidal silicaparticles in the invention refers to the particle diameter at the 50%point of the cumulative frequency in a particle size cumulative curveobtained by the volume standard.

Meanwhile, the average primary particle diameter of the colloidal silicaparticles can be measured using an electronic microscope (transmissiontype) or the like.

In addition, the average particle diameter of secondary particles formedby an assembly of some of the colloidal silica particles (averagesecondary particle diameter) represents the average particle diameterobtained in the particle size distribution obtained by the dynamic lightscattering method. Examples of measuring apparatuses that can be used toobtain the particle size distribution include LB-500 (manufactured byHoriba, Ltd.) and the like.

The content of the colloidal silica particles in the polishing fluid ofthe invention is preferably 0.5% by mass to 10% by mass, furtherpreferably 0.5% by mass to 8% by mass, and particularly preferably 1% bymass to 7% by mass with respect to the total mass of the polishing fluid(hereinafter, representing polishing fluids used for polishing, that is,diluted polishing fluids when polishing fluids are diluted by water oran aqueous solution. The “polishing fluids used for polishing” describedhereinafter also have the same meaning). That is, the content of thecolloidal silica particles is preferably 0.5% by mass or more from thestandpoint of polishing the second layer at a sufficient polishing rate,and is preferably 10% by mass or less from the standpoint of storagestability.

Abrasive grains other than the colloidal silica particles can be jointlyused in the polishing fluid of the invention as long as the effects ofthe invention are not impaired; however, even in such a case, thefraction of the colloidal silica particles exhibiting a negative ξpotential at the surfaces in the total abrasive grains is preferably 50%by mass or more, and particularly preferably 80% by mass or more. All ofthe abrasive grains included may be colloidal silica particlesexhibiting a negative ξ potential at the surfaces.

Examples of the abrasive grains that can be jointly used with thecolloidal silica particles in the polishing fluid of the inventioninclude fumed silica, ceria, alumina, titania, and the like. The size ofthe jointly used abrasive grains is preferably equal to or larger thanthat of the colloidal silica particles exhibiting a negative ξ potentialat the surfaces and equal to or smaller than double.

[Specific Inorganic Phosphate Compound]

The polishing fluid of the invention contains at least one inorganicphosphate compound selected from phosphoric acid (H₃PO₄), pyrophosphoricacid (H₄P₂O₇), and a polyphosphoric acid. Here, the polyphosphoric acidincludes condensed phosphoric acid (H_(n+2)P_(n)O_(3n+1)) andmethaphosphoric acid (HPO₃)_(n), wherein ‘n’ represents an integer of 3or larger.

When addition of the compound results in a relationship of (RRa)>(RRb),wherein ‘RRa’ is the polishing rate with respect to silicon nitride, and‘RRb’ is the polishing rate when the compound is not added, the compoundmay be defined as having a function of an accelerator with respect tosilicon nitride. Whether the compound has a function of the acceleratorwith respect to silicon nitride can be determined by the presence orabsence of the above relationship.

The inorganic phosphate compound included in the polishing fluid may beonly one or two or more. The content of the inorganic phosphate compoundin the polishing fluid is preferably 0.001% by mass to 15% by mass, morepreferably 0.005% by mass to 10% by mass, and further preferably 0.05%by mass to 5% by mass with respect to the mass of the polishing fluidused for polishing. That is, the content of the inorganic phosphatecompound is preferably the lower limit or higher from the standpoint ofachieving a sufficient polishing rate, and is preferably the upper limitor lower from the standpoint of maintaining a favorable flatness.

[Specific Anionic Surfactant]

The polishing fluid of the invention preferably contains at least one ofthe anionic surfactants represented by any of the following generalformulas (I) to (V).

R¹—SO₃X  (I)

[In the general formula, ‘R¹’ represents alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, all of which have acarbon number of 6 to 30, and groups formed by combining 2 or more ofthe above groups. ‘X’ represents a hydrogen atom, lithium, sodium,potassium, an ammonium cation, and quaternary ammonium cations.]

R¹—O—SO₃X  (II)

[In the general formula (II), ‘R¹’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups. ‘X’ represents a hydrogen atom, sodium, potassium,an ammonium cation, quaternary ammonium cations, diethanolamine, ortriethanolamine.]

R²—O—(CH₂CH₂O)_(n)—SO₃X  (III)

[In the general formula (III), ‘R²’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups. ‘n’ represents an integer of 1 to 10. ‘X’represents the same as in the general formula (II).]

[In the general formula (IV), ‘R³’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups, ‘X’ represents the same as in the general formula(II), and a plurality of Xs may be mutually the same or different.]

[In the general formula (V), ‘R⁴’ represents alkylene groups, alkynylenegroups, cycloalkylene groups, arylene groups, alkylene oxide groups, allof which have a carbon number of 1 to 20, or groups formed by combining2 or more of the above groups. ‘R⁵ to R⁹’ independently represent any ofa hydrogen atom, a hydroxyl group, alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, sulfo groups, carboxylgroups, all of which have a carbon number of 1 to 30, and hydrocarbongroups including the above. ‘X’ represents the same as in the generalformula (II).]

Specific examples of the anionic surfactant will be shown below. Theinvention is not limited to these compounds.

The number of the anionic surfactants that are used may be one or two ormore. The content of the anionic surfactant is preferably 0.001% by massto 1% by mass, more preferably 0.01% by mass to 1% by mass, and furtherpreferably 0.1% by mass to 1% by mass with respect to the mass of thepolishing fluid used for polishing. The content of the anionicsurfactant in the above range makes the effect of suppressing thepolishing rate of polysilicon favorable.

Here, the actions of the surfactant, including presumptions, will beoutlined. Since the surfaces of polysilicon are hydrophobic incomparison to other films, the surfactant can be absorbed. For example,it is presumed that, when the anionic surfactant is added, hydrophobicportions of the surfactant are disposed on the polysilicon surfaces, andanionic hydrophilic portions are disposed in a shape of facing outside.In summary, it is presumed that, when the anionic surfactant is added,an absorption layer is formed on the polysilicon surface, and thesurface electric charges are anionic. When colloidal silica particleshaving a negative ξ potential are present in such an absorption layer,it is presumed that a repulsive force is developed between the colloidalsilica particles and the polysilicon by the negative electric charges ofthe two. It is presumed that both this repulsive force and the action ofthe coexisting inorganic phosphate compound reduce the contact frequencybetween the two, and, consequently, the polishing rate is significantlysuppressed.

[Organic Acid]

In addition, other ordinary organic acids can be jointly used in thepolishing fluid of the invention as long as the effects of the inventionare not impaired.

The other organic acids are desirably water-soluble acids, and examplesthereof include water-soluble organic acids and amino acids. Moreappropriate examples of the organic acids and amino acids include onesselected from the following groups.

That is, examples of the organic acids include formic acid, acetic acid,propionic acid, butyric acid, valeric acid, 2-methyl butyric acid,n-hexanoic acid, 3,3-dimethylbutyrate, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoicacid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid,glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid,acidum tartaricum, citric acid, lactic acid, hydroxylethyl iminodiaceticacid, iminodiacetic acid, acetamido iminodiacetic acid,nitrilotripropanoic acid, nitrilotrimethylphosphoric acid,dihydroxyethyl glycine, tricine, salts, such as ammonium salts thereofor alkali metal salts, mixtures thereof, and the like.

In addition, examples of the amino acids include glycine, L-alanine,β-alanine, L-2-aminobutyric acid, L-norvaline, L-valine, L-leucine,L-norleucine, L-isoleucine, L-alloisoleucine, L-phenylalanine,L-proline, sarcosine, L-ornithine, L-lysine, taurine, L-serine,L-threonine, L-allothreonine, L-homoserine, L-tyrosine,3,5-diiodo-L-tyrosine, β-(3,4-dihydroxyphenyl)-L-alanine, L-thyroxin,4-hydroxy-L-proline, L-cysteine, L-methionine, L-ethionine,L-lanthionine, L-cystathionine, L-cystine, L-cysteic acid, L-asparagineacid, L-glutamic acid, S-(carboxylmethyl)-L-cystine, 4-aminobutyricacid, L-asparagine, L-glutamine, azaserine, L-arginine, L-canavanine,L-citrulline, δ-hydroxy-L-lysine, creatine, L-kynurenine, L-histidine,1-methyl-L-histidine, 3-methyl-L-histidine, ergothionein, L-triptophan,actinomycin C1, apamin, angiotensin angiotensin II, antipain, and thelike.

Furthermore, examples of organic acids that can be jointly used includenitrilotriacetic acid, diethylenetriamine pentaacetic acid,ethylenediaminetetraacetic acid, oxalic acid, malonic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalicacid, malic acid, tartaric acid, citric acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furan dicarboxylic acid, 3-furan carboxylic acid,2-tetrahydro furan carboxylic acid, diglycolic acid, methoxyacetic acid,methoxyphenyl acetic acid, phenoxyacetic acid, mixtures thereof, and thelike. Among the above, ethylenediaminetetraacetic acid, oxalic acid,malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, anddiglycolic acid are preferred from the standpoint of achieving afavorable selection ratio, and oxalic acid, adipic acid, pimelic acid,maleic acid, malic acid, tartaric acid, citric acid, and diglycol acidare more preferred.

When the other organic acids are jointly used, the total content of theorganic acids is preferably 0.01% by mass to 10% by mass, morepreferably 0.1% by mass to 10% by mass, and further preferably 0.5% bymass to 5% by mass with respect to the mass of the polishing fluid usedfor polishing.

[Other Components]

Arbitrary components other than the above essential components may beadded to the polishing fluid of the invention according to necessity.Hereinafter, other components that may be used arbitrarily will bedescribed.

(Corrosion Inhibitor)

A corrosion inhibitor, which is absorbed on a surface to be polished andforms a membrane, thereby suppressing corrosion of metal surfaces, maybe included in the polishing fluid of the invention. It is preferable toinclude a complex aromatic compound having 3 or more nitrogen atoms inthe molecule and a ring-fused structure as the corrosion inhibitor inthe invention. Here, the “3 or more nitrogen atoms” are preferably atomscomposing the fused ring, and such a complex aromatic compound ispreferably benzotriazole and a derivative formed by introducing avariety of substituent groups to benzotriazole.

Examples of the corrosion inhibitor that can be used in the inventioninclude benzotriazole (hereinafter also referred to as “BTA”),1,2,3-benzotriazole, 5,6-dimethyl-1,2,3-benzotriazole,1-(1,2-dicarboxyethyl)benzotriazole,1-[N,N-bis(hydroxyethyl)aminomethyl]benzotriazole,1-(hydroxymethyl)benzotriazole, and the like, and it is more preferableto select from 1,2,3-benzotriazole, 5,6-dimethyl-1,2,3-benzotriazole,1-(1,2-dicarboxyethyl)benzotriazole,1-[N,N-bis(hydroxyethyl)aminomethyl]benzotriazole, and1-(hydroxymethyl)benzotriazole among the above.

The added amount of the corrosion inhibitor is preferably 0.01% by massto 0.2% by mass, and further preferably 0.05% by mass to 0.2% by masswith respect to the mass of the polishing fluid used for polishing. Thatis, the added amount of the corrosion inhibitor is preferably 0.01% bymass or more from the standpoint of preventing the enlargement ofdishing, and is preferably 0.2% by mass or less from the standpoint ofstorage stability.

(Oxidant)

The polishing fluid of the invention may contain a compound thatoxidizes metal (oxidant), which is a polishing workpiece.

Examples of the oxidant include hydrogen peroxide, peroxide, nitrate,iodate, periodate, hypochlorite, chlorite, chlorate, perchlorate,persulfate, dichromate, permanganate, ozone water, silver (II) salt, andiron (III) salt, and hydrogen peroxide is preferably used.

Meanwhile, examples of the iron (III) salt that is preferably usedinclude organic complex salts of iron (III) as well as salts ofinorganic iron (III), such as iron (III) nitrate, iron (III) chloride,iron (III) sulfate, iron (III) bromide.

(pH Adjuster)

The polishing fluid of the invention needs to be pH 1.5 to 5.0. Thelower limit is not particularly limited as long as the limit is equal toor larger than the left value, but is preferably pH 1.5 or higher,further preferably pH 1.7 or higher, more preferably pH 1.8 or higher,and particularly preferably pH 2.0 or higher. The upper limit is alsonot limited, but is preferably pH 4.5 or lower, and more preferably pH4.0 or lower. The polishing fluid of the invention exhibits excellenteffects with the pH in the above range.

Alkali/acid or a buffer is used in order to adjust the pH of thepolishing fluid to the above range.

Preferable examples of the alkali/acid or the buffer include ammonia,ammonium hydroxide, and organic ammonium hydroxides, such as tetramethylammonium hydroxide; nonmetallic alkali agents, such as alkano lamines,such as diethanolamine, triethanolamine, and triisopropanolamine; alkalimetal hydroxides, such as sodium hydroxide, potassium hydroxide, andlithium hydroxide; inorganic acids, such as nitric acid, sulfuric acid,and phosphoric acid; carbonates, such as sodium carbonate; phosphates,such as trisodium phosphate; borate, tetraborate, and hydroxylbenzoate.Particularly preferable examples of the alkali agents include ammoniumhydroxide, potassium hydroxide, lithium hydroxide, and tetramethylammonium hydroxide.

The added amount of the alkali/acid or the buffer may be any amount aslong as the pH is maintained in the preferable range, but is preferably0.0001 moles to 1.0 mole, and more preferably 0.003 moles to 0.5 molesin 1 L of the polishing fluid used for polishing. Meanwhile, the pH inthe invention is measured by the measuring method as employed in theexamples below unless otherwise described.

(Chelating Agent)

The polishing fluid of the invention preferably contains a chelatingagent (that is, a water softener) according to necessity in order toreduce the adverse effects of interfused multivalent metal ions or thelike.

The chelating agent is a commonly used water softener, which is aprecipitation inhibitor of calcium or magnesium, or related compoundsthereof. Examples of the chelating agent include nitrilotriacetic acid,diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid,N,N,N-aminotrimethylene phosphonic acid,ethylenediamine-N,N,N′,N′-tetramethylene sulfonic acid,transcyclohexanediaminetetraacetic acid, 1,2-diaminopropane tetraaceticacid, glycol ether diamine tetraacetic acid, ethylenediamineortho-hydroxyphenyl acetic acid, (S,S)-ethylenediamine disuccinic acid,N-(2-carboxylate ethyl)-L-asparagine acid, β-alanine diacetic acid,2-phosphonobutane-1,2,4-tricarboxylic acid,1-hydroxyethylidene-1,1-diphosphoric acid,N,N′-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid,1,2-dihydroxybenzene-4,6-disulfonic acid, and the like.

Two or more of the chelating agents may be jointly used according tonecessity.

The added amount of the chelating agent may be any amount as long as theamount is enough to block metal ions, such as interfusing multivalentmetal ions, and, for example, the chelating agent is added to be 0.0003moles to 0.07 moles in 1 L of the polishing fluid used for polishing.

[Semiconductor Substrate (Polishing Workpiece)]

A polishing workpiece to which the polishing fluid of the invention ispreferably applied is a polishing workpiece (semiconductor substrates)that is configured to have at least a first layer 1 includingpolysilicon or modified polysilicon, and a second layer 2 including atleast one selected from a group consisting of silicon oxide, siliconnitride, silicon carbide, silicon carbonitride, silicon oxycarbide, andsilicon oxynitride (refer to FIG. 1). In more detail, the workpiece is apreferably used workpiece when polysilicon or modified polysilicon isapplied as an electrode material, and a gate electrode is formed by theCMP in a semiconductor integrated circuit.

Meanwhile, the “modified polysilicon” in the invention includes siliconobtained by doping impurity elements, such as boron (B) or phosphorous(P), in polysilicon.

In general, when a gate electrode is formed, a layer made of siliconoxide and the like is formed on the surface of the substrate, recessportions are formed on the layer by etching or the like, the formedrecess portions are filled with polysilicon or modified polysilicon,thereby forming a first layer 1. Next, a second layer 2 including atleast one selected from a group consisting of silicon oxide, siliconnitride, silicon carbide, silicon oxynitride, silicon oxycarbide, andsilicon carbonitride is laminated on the surface of the first layer as abarrier layer.

In the CMP used for the formation of the gate electrode, polishingbegins from the surface of the second layer 2, polishing of the secondlayer 2 proceeds, and the polishing rate abruptly decreases when thesurface of the first layer 1 is exposed, thereby detecting that thepolishing of the second layer 2 is finished, and excessive polishing ofthe surface 11 of polysilicon or modified polysilicon used for the gateelectrode is suppressed with respect to the second layer surface 21 ofthis moment. The modified polysilicon represents polysilicon obtained bydoping impurities, such as B or P, in polysilicon.

After that, polysilicon or modified polysilicon which functions as theelectrode and places other than the necessary silicon oxide layer in theperipheral portion are removed by etching so as to form the gateelectrode.

Meanwhile, in FIG. 1, ‘1’ is the first layer, ‘2’ is the second layer,‘3’ is a third layer (SiN layer), ‘4’ is a dielectric layer (low-kmaterial layer), ‘51’ is a n-type semiconductor layer, ‘52’ is a p-typesemiconductor layer, ‘6’ is a Si substrate, ‘7’ is an insulator layer,‘11’ is a polished first layer surface, and ‘21’ is a polished secondlayer surface. ‘d’ is the polishing depth, ‘S₁’ is a third layer topsurface, and ‘S₂’ is a first layer top surface.

[Electrical Conductivity]

The electrical conductivity of the polishing fluid of the invention ispreferably 0.01 (mS/cm) to 12 (mS/cm), more preferably 1 (mS/cm) to 12(mS/cm), and particularly preferably 3 (mS/cm) to 10 (mS/cm). A methodof measuring the electrical conductivity is not particularly limited,but the method as described in the examples below will be employedunless otherwise described.

[Polishing Method]

The polishing method of the invention is a method in which the polishingfluid of the invention as described above is used and supplied to apolishing pad on a polishing platen, and the polishing platen is rotatedso that the polishing pad is relatively moved while in continuouscontact with the surface to be polished of a polishing workpiece,thereby performing polishing.

The polishing fluid of the invention is made into a fluid to be used: 1by using a concentrated solution as the polishing fluid and diluting thepolishing fluid by adding water or an aqueous solution when used; 2 bypreparing each of the components in the aqueous solution form asdescribed in the next section, mixing the solutions, and diluting thepolishing fluid by adding water according to necessity; and 3. bypreparing the polishing fluid as a fluid to be used. The polishing fluidof any case can be applied to the polishing method of the invention.

Ordinary polishing apparatuses having a holder that supports a polishingworkpiece (for example, a wafer having a conductive material film formedthereon and the like) having a surface to be polished and a polishingplaten (having a motor or the like capable of varying the rotationfrequency mounted therein) to which a polishing pad is attached can beused as an apparatus used for polishing. Examples of the polishing padthat can be used include ordinary nonwoven fabrics, expandedpolyurethane, porous fluororesins, and the like, and are notparticularly limited. In addition, the polishing conditions are notparticularly limited, but the rotation speed of the polishing platen ispreferably a low rotation of 200 rpm or less so that a polishingworkpiece does not fly away. The pressure that presses a polishingworkpiece having a surface to be polished (a film to be polished) to thepolishing pad is preferably 0.68 kPa to 34.5 kPa, and more preferably3.40 kPa to 20.7 kPa in order to satisfy the evenness of polishing rateinside the surface of the polishing workpiece and the flatness of apattern.

The polishing fluid is continuously supplied to the polishing pad by apump or the like during polishing.

After the completion of polishing, the polishing workpiece is washedwell in flowing water, shaken to remove water droplets attached to thepolishing workpiece, and dried using a spin dryer and the like.

When the concentrated solution is diluted as described in the abovemethod 1 in the invention, the aqueous solution described below can beused. The aqueous solution is water already containing at least one ofan oxidant, an organic acid, an additive, and a surfactant, and thetotal components of the components included in the aqueous solution andthe components included in the concentrated solution to be dilutedbecome the components of the polishing fluid used for polishing (fluidto be used).

Since components that are difficult to dissolve can be combinedafterward in the aqueous solution form when the concentrated solution isdiluted by the aqueous solution before use, a concentrated solution thatis more concentrated can be manufactured.

Examples of a method for diluting the concentrated solution by addingwater or an aqueous solution include a method in which the concentratedpolishing fluid and water or an aqueous solution are mixed by joiningthe pipe supplying the concentrated polishing fluid and the pipesupplying water or an aqueous solution in the middle, and the fluid tobe used of the mixed and diluted polishing fluid is supplied to thepolishing pad. Methods that are usually carried out, such as a method inwhich the two fluids are collided and mixed through narrow passages in astate of pressure being applied, a method in which glass tubes and thelike in the pipe are filled with a filler so that the flows of thefluids are repeatedly separated and joined, and a method in whichpower-rotated blades are provided in the pipe, can be employed for themixing of the concentrated fluid and water or an aqueous solution.

The supply rate of the polishing fluid is preferably 10 ml/min to 1000ml/min, and more preferably 170 ml/min to 800 ml/min to satisfy theevenness of polishing rate inside the surface to be polished and theflatness of a pattern.

Furthermore, examples of a method of polishing while the concentratedsolution is continuously diluted by water, an aqueous solution, or thelike include a method in which a pipe supplying the polishing fluid anda pipe supplying water or an aqueous solution are independentlyprovided, a predetermined amount of the fluid is supplied to a polishingpad from each of the pipes, and polishing is carried out while the twoare mixed by the relative movement of the polishing pad and the surfaceto be polished. In addition, a method in which a predetermined amount ofthe concentrated solution and a predetermined amount of water or anaqueous solution are fed and mixed in a vessel, and the mixed polishingfluid is supplied to a polishing pad, thereby performing polishing, canalso be used.

In addition, another example of the polishing method includes a methodin which the components that the polishing fluid should contain aredivided into at least two constituent components, the constituentcomponents are diluted by adding water or an aqueous solution when used,supplied to the polishing pad on the polishing platen, brought intocontact with the surface to be polished, and polishing is carried out bythe relative movement of the surface to be polished and the polishingpad.

In addition, low-solubility additives are divided into two constituentcomponents (A) and (B). For example, an oxidant, an additive, and asurfactant belong to the constituent component (A), and an organic acid,an additive, a surfactant, and water belong to the constituent component(B), water or an aqueous solution is added when the above are used, andthe constituent component (A) and the constituent component (B) arediluted and used.

In the case of the above example, three pipes supplying the constituentcomponent (A), the constituent component (B), and water or an aqueoussolution are required respectively, and dilution mixing can be done by amethod in which the three pipes are joined to one pipe supplying thepolishing fluid to the polishing pad, and mixing is performed inside thepipe. In this case, it is possible to join two pipes and then join theremaining pipe. Specifically, in the method, the constituent componentincluding an additive that is difficult to dissolve and otherconstituent components are mixed, a mixing passage is elongated so as tosecure a dissolution time, and, furthermore, the pipe of water or anaqueous solution is joined.

Other mixing methods include a method in which each of the three pipesis directly connected to the polishing pad, and mixing is carried out bythe relative movement of the polishing pad and the surface to bepolished, and a method in which the three constituent components aremixed in a vessel, and the diluted polishing fluid is supplied to thepolishing pad from the vessel.

In the polishing method described above, it is possible to make one ofthe constituent components including an oxidant 40° C. or lower and heatthe other constituent component to a range of 100° C. from roomtemperature, thereby making the fluid temperature 40° C. or lower whenthe first constituent component and the second constituent component aremixed or when water or an aqueous solution is added so as to dilute theconcentrated solution. This method is a preferable method for increasingthe solubility of the raw material of the polishing fluid having a lowsolubility by using a phenomenon in which the solubility increases asthe temperature is high.

Since the raw material dissolved by heating the second constituentcomponent to a range of 100° C. from room temperature is precipitated inthe solution when the temperature decreases, it is necessary to performheating in advance so as to dissolve the precipitated raw material whenthe second constituent component is used in a low-temperature state. Forthis, it is possible to employ means for heating and sending the fluidof the second constituent component in which the raw material isdissolved and means for stirring the fluid including the precipitates,sending the fluid, and heating the pipe so as to dissolve theprecipitates. Since there is a concern of decomposition of the oxidantwhen the temperature of the first constituent component including theoxidant is increased to 40° C. or higher, it is preferable to mix theheated second constituent component and the first constituent componentincluding the oxidant at 40° C. or lower.

As such, in the invention, the components of the polishing fluid may bedivided into two or more groups and supplied to the surface to bepolished. In this case, it is preferable to divide and supply thecomponents including oxides and the components including organic acids.In addition, it is also possible to make the polishing fluid into aconcentrated solution and separately supply dilution water to thesurface to be polished.

In the invention, when a method in which the components of the polishingfluid are divided into two or more groups and supplied to the surface tobe polished is applied, the supplied amount represents the sum of thesupplied amounts from the respective pipes.

[Pad]

The polishing pad for polishing to which the polishing method of theinvention can be applied may be a nonfoam-structured pad or afoam-structured pad. The former is a pad for which a hard syntheticresin bulk material, such as a plastic plate, is used. In addition, thelatter includes an independent foam (dry foam-based), a continuous foam(wet foam-based), and a bilayer complex (lamination-based), and thebilayer complex (lamination-based) is particularly preferred. The foammay be homogeneous or inhomogeneous.

Furthermore, the pad may contain abrasive grains (for example, ceria,silica, alumina, a resin, and the like) that are usually used forpolishing. In addition, there are hard pads and soft pads with regard tothe hardness, and the pad may be any of the two. It is preferable to usea pad having different hardnesses in the respective layers among thelamination-based pads. Preferable examples of materials include nonwovenfabrics, artificial leather, polyamide, polyurethane, polyester,polycarbonate, and the like. In addition, processing of latticegrooves/holes/concentric grooves/spiral grooves, and the like may becarried out on the surface that is brought into contact with the surfaceto be polished.

[Wafer]

The diameter of a wafer, which is a polishing workpiece as a subject ofthe CMP carried out using the polishing fluid of the invention, ispreferably 200 mm or larger, and particularly preferably 300 mm orlarger. When the diameter is 300 mm or larger, the effects of theinvention are significantly exhibited.

[Polishing Apparatus]

Apparatuses that can carry out polishing using the polishing fluid ofthe invention are not particularly limited, and examples thereof includeMA-300D (manufactured by Musashino Electronics Co., Ltd.), Mirra MesaCMP, Reflexion CMP (Applied Materials, Inc.), FREX 200, FREX 300 (EbaraCorporation), NPS 3301, NPS 2301 (Nicon Corporation), A-FP-310A,A-FP-210A (Tokyo Seimitsu Co., Ltd.), 2300 TERES (Wolfram Research),Momentum (Speedfam IPEC), and the like.

Hereinafter, the invention will be described in more detail usingexamples, but the invention is not limited to the following exampleswithin the scope of the gist of the invention.

Example 1 Preparation of a Polishing Fluid

Polishing fluids having the compositions and pH shown in Table 1 wereprepared. Moreover, in addition to the respective components shown inthe table, ammonia water and nitric acid are added so as to make the pHdescribed in the table, and pure water was added so as to make a totalweight of 1,000 mL.

Colloidal silica particles (A1 to A9) used in each of the examples inthe specification are shown in the following Table A. Furthermore, A1 toA9 are manufactured by Fusou Chemical Co., Ltd. Furthermore, the averageprimary particle diameters and the average secondary particle diametersin Table A are average values measured as a result of observing polishedparticles using a SEM.

TABLE A Average Average Abrasive primary secondary grain particleparticle particle Product name diameter (nm) diameter (nm) A1 PL3 35 70A2 PL3L 35 — A3 PL3H 25 75 A4 PL2 25 45 A5 PL2L 25 — A6 PL2H 20 40 A7PL1 15 25 A8 PL1H 10 25 A9 PL3 (anion zole) 35 70

TABLE B Abrasive * Adjustment of pH of each grain particle ξ potential(mV) original fluid using nitric acid A1 2.7 mV (near pH 2.0) A2 2.6 mV(near pH 2.0) A3 3.0 mV (near pH 2.0) A4 2.8 mV (near pH 2.0) A5 2.5 mV(near pH 2.0) A6 3.0 mV (near pH 2.0) A7 1.5 mV (near pH 2.0) A8 2.0 mV(near pH 2.0) A9 −20 mV  (near pH 2.0)

<Evaluation Method>

—Polishing Apparatus—

The wafer shown below was polished as a polishing subject under thefollowing conditions using “MA-300D,” manufactured by MusashinoElectronics Co., Ltd., as a polishing apparatus while a slurry wassupplied under the following conditions, and the evaluation of thepolishing fluid was carried out.

Table rotation frequency: 112 rpm

Head rotation frequency: 113 rpm

Polishing pressure: 18.4 kPa

Polishing pad: IC1400 XY-K-Pad, manufactured by Rodel-Nitta Corporation

Polishing fluid supply rate: 50 ml/min

—Polishing Subject—

An 8-inch wafer having a polysilicon layer (p-Si layer) as the firstlayer, a silicon oxide layer (Si)₂ layer) as the second layer, and asilicon nitride layer (Si₃N₄ layer) as the third layer respectivelyformed on a Si substrate as shown in FIG. 1 was cut into 6 cm×6 cm, andthe cut wafer was used as a polishing subject.

—Polishing Rate, Polishing Rate Ratio—

The polishing rate was computed by measuring the layer thicknesses (nm)before and after polishing for each of the polysilicon layer (p-Silayer), the silicon oxide layer (SiO₂ layer), and the silicon nitridelayer (Si₃N₄ layer), and using the following formula. Meanwhile, thelayer thickness was measured using a noncontact-type film thicknessmeasuring apparatus FE-33 (manufactured by Otsuka Electronics Co.,Ltd.).

Polishing rate (nm/min)=(film thickness before polishing−film thicknessafter polishing)/polishing time

In addition, the polishing rate ratios represented by RR (other)/RR(p-Si) were computed for p-Si layer to SiO₂ layer and p-Si layer toSi₃N₄ layer.

The obtained results are shown in Table 1.

—Aging Stability—

The aging stability was compared by forcibly heating each of thepolishing fluids under the condition of 60° C. for 2 weeks, and thenmeasuring the average particle diameter (MPS) of the colloidal silicaparticles before and after aging. Meanwhile, the average particlediameter (MPS) was measured using a dynamic light scattering-typeparticle size distribution measuring apparatus LB-500 (manufactured byOtsuka Electronics Co., Ltd.).

AA: alteration from before to after aging is 3% or lower, and stabilityis extremely high.A: alteration from before to after aging is 5% or lower, and stabilityis high.B: alteration from before to after aging is 10% or lower, and there is aconcern regarding stability (on a level of no practical problem).C: alteration from before to after aging is 10% or higher, and there isa problem of stability (on a level where practical use is impossible).

—ξ Potential—

The ξ potential of the particle was measured by the following method.

Here, in the invention, the ξ potential at the surface of the colloidalsilica particle was evaluated by measuring the original fluid of theevaluation fluid using DT-1200 (manufactured by Nihon Rufuto Co., Ltd.).

—pH—

The pHs in the tables are values measured at room temperature (20° C.)using F-51 (trade name, manufactured by Horiba, Ltd.)

—Electrical Conductivity—

Here, in the invention, the electrical conductivity of the polishingfluid was evaluated by measuring the original fluid of the evaluationfluid using an electrical conductivity meter GM-60G (TOA-DKK).

TABLE 1 Polishing Si₃N₄ Ox Poly-Si Si₃N₄ particle Anionic Other PR RR RRRR/ Ox RR/ (content_particle Accelerator surfactant additives (nm/ (nm/(nm/ poly-Si poly-Si Aging Specimen diameter) (content) (content)(content) pH min) min) min) RR RR stability 101 A1 Inorganic phosphoricP2 1.5 75 82 6 12.50 13.67 AA (150 g/L) acid (5 g/L) (0.5 g/L) 102 A1Inorganic phosphoric P2 2.0 78 80 5 15.60 16.00 AA (150 g/L) acid (5g/L) (0.5 g/L) 103 A1 Inorganic phosphoric P2 2.5 65 58 7 9.29 8.29 AA(150 g/L) acid (5 g/L) (0.5 g/L) 104 A1 Inorganic phosphoric P2 3.0 5347 9 5.89 5.22 AA (150 g/L) acid (5 g/L) (0.5 g/L) 105 A1 Inorganicphosphoric P2 4.0 40 36 8 5.00 4.50 A (150 g/L) acid (5 g/L) (0.5 g/L)106 A1 Inorganic phosphoric P2 4.5 35 35 13 2.69 2.69 A (150 g/L) acid(5 g/L) (0.5 g/L) c11 A1 Inorganic phosphoric P2 7.0 15 18 25 0.60 0.72C (150 g/L) acid (5 g/L) (0.5 g/L) c12 A1 Inorganic phosphoric P2 10.0 830 70 0.11 0.43 B (150 g/L) acid (5 g/L) (0.5 g/L) 201 A2 Inorganicphosphoric P2 2.0 65 68 12 5.42 5.67 AA (150 g/L) acid (5 g/L) (0.5 g/L)202 A3 Inorganic phosphoric P2 2.0 70 71 4 17.50 17.75 AA (150 g/L) acid(5 g/L) (0.5 g/L) 203 A4 Inorganic phosphoric P2 2.0 72 68 4 18.00 17.00AA (150 g/L) acid (5 g/L) (0.5 g/L) 204 A5 Inorganic phosphoric P2 2.058 53 8 7.25 6.63 AA (150 g/L) acid (5 g/L) (0.5 g/L) 205 A6 Inorganicphosphoric P2 2.0 61 63 3 20.33 21.00 AA (150 g/L) acid (5 g/L) (0.5g/L) 206 A7 Inorganic phosphoric P2 2.0 49 39 3 16.33 13.00 AA (150 g/L)acid (5 g/L) (0.5 g/L) 207 A8 Inorganic phosphoric P2 2.0 30 25 3 10.008.33 AA (150 g/L) acid (5 g/L) (0.5 g/L) 208 A9 Inorganic phosphoric P22.0 80 65 2 40.00 32.50 AA (150 g/L) acid (5 g/L) (0.5 g/L) c22 NoneInorganic phosphoric P2 2.0 0 0 0.3 — — AA acid (5 g/L) (0.5 g/L) 301 A1Inorganic phosphoric P2 2.0 58 65 4 14.50 16.25 AA (150 g/L) acid (0.05g/L) (0.5 g/L) 302 A1 Inorganic phosphoric P2 2.0 72 71 5 14.40 14.20 AA(150 g/L) acid (0.5 g/L) (0.5 g/L) 303 A1 Inorganic phosphoric P2 2.0 7979 5 15.80 15.80 AA (150 g/L) acid (2 g/L) (0.5 g/L) 304 A1 Inorganicphosphoric P2 2.0 80 79 4 20.00 19.75 A (150 g/L) acid (10 g/L) (0.5g/L) 305 A1 Inorganic phosphoric P2 2.0 76 80 5 15.20 16.00 A (150 g/L)acid (50 g/L) (0.5 g/L) 306 A1 Inorganic P2 3.0 54 63 5 10.80 12.60 AA(150 g/L) pyrophosphoric (0.5 g/L) acid (0.8 g/L) 307 A1 Inorganic P23.0 71 75 6 11.83 12.50 A (150 g/L) pyrophosphoric (0.5 g/L) acid (8g/L) 308 A1 Inorganic P2 2.0 45 51 5 9.00 10.20 AA (150 g/L)polyphosphoric (0.5 g/L) acid (0.1 g/L) 309 A1 Inorganic P2 2.0 68 66 513.60 13.20 A (150 g/L) polyphosphoric (0.5 g/L) acid (1 g/L) 310 A1Inorganic P2 2.0 70 68 6 11.67 11.33 A (150 g/L) polyphosphoric (0 .5g/L) acid (10 g/L) c31 A1 None P2 2.0 11 13 10 1.10 1.30 A (150 g/L)(0.5 g/L) 401 A1 Inorganic phosphoric P2 2.0 78 80 8 9.75 10.00 AA (150g/L) acid (5 g/L) (0.05 g/L) 402 A1 Inorganic phosphoric P2 2.0 78 80 326.00 26.67 A (150 g/L) acid (5 g/L) (5.0 g/L) 403 A1 Inorganicphosphoric P1 3.0 51 46 10 5.10 4.60 AA (150 g/L) acid (5 g/L) (0.2 g/L)404 A1 Inorganic phosphoric P3 4.0 39 36 9 4.33 4.00 AA (150 g/L) acid(5 g/L) (0.5 g/L) 405 A1 Inorganic phosphoric P4 3.0 53 47 10 5.30 4.70AA (150 g/L) acid (5 g/L) (0.5 g/L) 406 A1 Inorganic phosphoric P9 2.078 80 7 11.14 11.43 A (150 g/L) acid (5 g/L) (0.5 g/L) c41 A1 Inorganicphosphoric None 5.5 38 28 35 1.09 0.80 AA (150 g/L) acid (5 g/L) 501 A1Inorganic phosphoric P2 Sulfuric 2.0 84 85 5 17.00 17.00 AA (150 g/L)acid (5 g/L) (0.5 g/L) acid (2 g/L) 502 A1 Inorganic phosphoric P2Ethane 2.0 82 83 4 20.75 20.75 AA (150 g/L) acid (5 g/L) (0.5 g/L)sulfonic acid (2 g/L) 503 A1 Inorganic phosphoric P2 Taurine 2.0 83 52 510.40 10.40 AA (150 g/L) acid (5 g/L) (0.5 g/L) (2 g/L) 504 A1 Inorganicphosphoric P2 p-toluene 2.0 85 81 5 16.20 16.20 AA (150 g/L) acid (5g/L) (0.5 g/L) sulfonic acid (2 g/L) c51 A1 1-hydroxy-1,1- P2 2.0 79 815 16.20 16.20 A (150 g/L) diphosphoric (0.5 g/L) acid (10 g/L) 601 A1Inorganic phosphoric 2.0 72 82 14 5.14 5.86 AA (150 g/L) acid (5 g/L)602 A1 Inorganic phosphoric 2.5 78 78 13 6.00 6.00 AA (150 g/L) acid (5g/L) 603 A1 Inorganic phosphoric 3.0 74 72 12 6.17 6.00 AA (150 g/L)acid (5 g/L) 604 A1 Inorganic phosphoric 2.0 75 85 15 5.00 5.67 AA (150g/L) acid (2 g/L) 605 A1 Inorganic phosphoric 2.0 102 140 18 5.67 7.78AA (300 g/L) acid (5 g/L)

TABLE 2 Polishing fluid specimen No. Electrical conductivity (mS/cm) 1016.20 102 6.46 103 7.23 c11 23.5 c12 32.5 201 6.46 202 6.45 203 6.46 c225.53 301 5.59 302 5.45 303 5.83 c31 1.08 401 6.15 402 6.89 403 6.55 c416.35 501 9.56 502 9.12 503 9.83 c51 15.6 601 6.43 602 6.13 603 5.99

1. A polishing fluid used for the chemical mechanical polishing ofsemiconductor substrates that are configured to have at least a firstlayer including polysilicon or modified polysilicon, and a second layerincluding at least one selected from a group consisting of siliconoxide, silicon nitride, silicon carbide, silicon carbonitride, siliconoxycarbide, and silicon oxynitride, wherein each of the componentsrepresented by the following (1) and (2) is included, the pH is 1.5 to5.0, and a polishing workpiece can be polished in a range of a ratiorepresented by RR (other)/RR (p-Si) when the polishing rate of the firstlayer is RR (p-Si), and the polishing rate of the second layer is RR(other) of 1.5 to
 200. (1) Colloidal silica particles (2) At least oneinorganic phosphate compound selected from phosphoric acid,pyrophosphoric acid, and polyphosphoric acid.
 2. The polishing fluidaccording to claim 1, further including an anionic surfactantrepresented by the general formula (I) as a third component.R¹—SO₃X  (I) [In the general formula, ‘R¹’ represents alkyl groups,alkenyl groups, cycloalkyl groups, aryl groups, aralkyl groups, all ofwhich have a carbon number of 6 to 30, and groups formed by combining 2or more of the above groups. ‘X’ represents a hydrogen atom, lithium,sodium, potassium, an ammonium cation, and quaternary ammonium cations.]3. The polishing fluid according to claim 2, including at least oneselected from a group consisting of compounds represented by thefollowing general formula (II), general formula (III), general formula(IV), and general formula (V) instead of or together with the anionsurfactant represented by the general formula (I) as the thirdcomponent.R¹—O—SO₃X  (II) [In the general formula (II), ‘R¹’ represents alkylgroups, alkenyl groups, cycloalkyl groups, aryl groups, aralkyl groups,all of which have a carbon number of 6 to 30, or groups formed bycombining 2 or more of the above groups. ‘X’ represents a hydrogen atom,sodium, potassium, an ammonium cation, quaternary ammonium cations,diethanolamine, or triethanolamine.]R²—O—(CH₂CH₂O)_(n)—SO₃X  (III) [In the general formula (III), ‘R²’represents alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups,aralkyl groups, all of which have a carbon number of 6 to 30, or groupsformed by combining 2 or more of the above groups. ‘n’ represents aninteger of 1 to
 10. ‘X’ represents the same as in the general formula(II).]

[In the general formula (IV), ‘R³’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups, ‘X’ represents the same as in the general formula(II), and a plurality of Xs may be mutually the same or different.]

[In the general formula (V), ‘R⁴’ represents alkylene groups, alkynylenegroups, cycloalkylene groups, arylene groups, alkylene oxide groups, allof which have a carbon number of 1 to 20, or groups formed by combining2 or more of the above groups. ‘R⁵ to R⁹’ independently represent any ofa hydrogen atom, a hydroxyl group, alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, sulfo groups, carboxylgroups, all of which have a carbon number of 1 to 30, and hydrocarbongroups including the above. ‘X’ represents the same as in the generalformula (II).]
 4. The polishing fluid according to claim 1, wherein theconcentration of the colloidal silica particles is 0.1% by mass to 10%by mass with respect to the total mass of the polishing fluid.
 5. Thepolishing fluid according to claim 1, wherein the average primaryparticle diameter of the colloidal silica particles is 5 nm to 100 nm,and the average secondary particle diameter is in a range of 10 nm to300 nm.
 6. The polishing fluid according to claim 1, wherein thecolloidal silica particles have a negative ξ potential, and the ξpotential is −50 mV to −5 mV.
 7. The polishing fluid according to claim1, wherein the content of the inorganic phosphate compound is 0.001% bymass to 10% by mass.
 8. The polishing fluid according to claim 2,wherein the concentration of the anionic surfactant is 0.001% by mass to1% by mass with respect to the total mass of the polishing fluid.
 9. Thepolishing fluid according to claim 2, wherein the anionic surfactant isa multivalent anionic surfactant.
 10. The polishing fluid according toclaim 1, wherein the electrical conductivity of the polishing fluid isin a range of 0.01 (mS/cm) to 12 (mS/cm).
 11. A method of manufacturinga semiconductor device, wherein, each time the chemical mechanicalpolishing (CMP) method is carried out to polish the surface of asemiconductor substrate that is configured to have at least a firstlayer including polysilicon or modified polysilicon, and a second layerincluding at least one selected from a group consisting of siliconoxide, silicon nitride, silicon carbide, silicon carbonitride, siliconoxycarbide, and silicon oxynitride, a processing treatment including (a)a step in which a polishing fluid including each of the components ofthe following (1) and (2) and having a pH of 1.5 to 5.0 is prepared, (b)a step in which the polishing fluid is supplied to the surface of thesemiconductor substrate, and a polishing pad is brought into contactwith the surface of the semiconductor substrate, and (c) a step inwhich, each time the first layer and the second layer of thesemiconductor substrate are polished, the polishing pad and thesemiconductor substrate are relatively moved so that a polishingworkpiece can be polished in a range of a ratio represented by RR(other)/RR (p-Si) when the polishing rate of the first layer is RR(p-Si), and the polishing rate of the second layer is RR (other) of 1.5to 200 while the polishing pad is in continuous contact with the surfaceof the semiconductor substrate through the polishing fluid for a timesufficient enough to polish the second layer is carried out. (1)Colloidal silica particles (2) At least one inorganic phosphate compoundselected from phosphoric acid, pyrophosphoric acid, and polyphosphoricacid.
 12. The method of manufacturing a semiconductor device accordingto claim 11, further including compounds selected from a groupconsisting of compounds represented by the general formulas (I) to (V)as a third component.R¹—SO₃X  (I) [In the general formula, ‘R¹’ represents alkyl groups,alkenyl groups, cycloalkyl groups, aryl groups, aralkyl groups, all ofwhich have a carbon number of 6 to 30, and groups formed by combining 2or more of the above groups. ‘X’ represents a hydrogen atom, lithium,sodium, potassium, an ammonium cation, and quaternary ammonium cations.]R¹—O—SO₃X  (II) [In the general formula (II), ‘R¹’ represents the sameas the general formula (I). ‘X’ represents a hydrogen atom, sodium,potassium, an ammonium cation, quaternary ammonium cations,diethanolamine, or triethanolamine.]R²—O—(CH₂CH₂O)_(n)—SO₃X  (III) [In the general formula (III), ‘R²’represents alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups,aralkyl groups, all of which have a carbon number of 6 to 30, or groupsformed by combining 2 or more of the above groups. ‘n’ represents aninteger of 1 to
 10. ‘X’ represents the same as in the general formula(II).]

[In the general formula (IV), ‘R³’ represents alkyl groups, alkenylgroups, cycloalkyl groups, aryl groups, aralkyl groups, all of whichhave a carbon number of 6 to 30, or groups formed by combining 2 or moreof the above groups, ‘X’ represents the same as in the general formula(II), and a plurality of Xs may be mutually the same or different.]

[In the general formula (V), ‘R⁴’ represents alkylene groups, alkynylenegroups, cycloalkylene groups, arylene groups, alkylene oxide groups, allof which have a carbon number of 1 to 20, or groups formed by combining2 or more of the above groups. ‘R⁵ to R⁹’ independently represent any ofa hydrogen atom, a hydroxyl group, alkyl groups, alkenyl groups,cycloalkyl groups, aryl groups, aralkyl groups, sulfo groups, carboxylgroups, all of which have a carbon number of 1 to 30, and hydrocarbongroups including the above. ‘X’ represents the same as in the generalformula (II).]